Technical Abstract:
We investigated the effect of established perennial plants on growth of the invasive annual grass Bromus tectorum L. (cheatgrass, downy brome). Seeds of B. tectorum were planted between two established plants (competition) and individually (no competition) in separate (4 replicates) rhizotrons (30 cm x 10 cm x 100 cm deep), using the A horizon of a fine sandy loam field soil presently invaded by B. tectorum. Perennial plants used were Achnatherum hymenoides (Indian ricegrass), Leymus triticoides (Creeping wildrye), and Elymus wawawaiensis (Snake River wheatgrass). Treatments for each growth cycle (90 days) were as follows: 1st cycle – no trimming of established perennials before planting of B. tectorum; 2nd – established plants trimmed at 5 cm immediately before planting; 3rd – plants trimmed and activated charcoal mixed with soil between established plants before planting; 4th – plants trimmed and soil top dressed with complete fertilizer before planting. Throughout the experiment, all rhizotrons were placed in plastic buckets and kept continually watered from beneath and periodically watered from above with dionized water. Relative to B. tectorum plants grown individually, growth between established perennials significantly reduced the growth of B. tectorum. Fertilizer application significantly increased the N concentration of B. tectorum, but did not significantly increase its growth. Our data suggest that competition with established plants greatly reduces the growth of B. tectorum. The reduced growth is not a function of water or nutrient limitation, nor allelopathic agents that could be removed with activated charcoal.